Progressive Multifocal Leukoencephalopathy after Natalizumab Monotherapy

This report describes progressive multifocal leukoencephalopathy in a patient who was receiving natalizumab therapy for multiple sclerosis. Plasma exchange was used to accelerate the clearance of natalizumab. Three weeks after plasma exchange, the patient's condition worsened neurologically because of the development of an immune-reconstitution inflammatory syndrome, but his condition improved after several weeks. This report describes PML in a patient who was receiving natalizumab therapy for multiple sclerosis. Three weeks after treatment with plasma exchange, the patient's condition worsened neurologically because of the development of an immune-reconstitution inflammatory syndrome. PML is a rare, opportunistic, demyelinating viral infection of the central nervous system caused by JC virus, a human polyomavirus. It usually occurs in patients with profound immunosuppression. 1 Natalizumab, a monoclonal antibody against α 4 integrins, reduces the extravasation of T lymphocytes, B lymphocytes, and plasma cells into the central nervous system. 2 The drug effectively decreases the number of multiple sclerosis lesions on MRI and the number of clinical relapses. 3 , 4 The use of antibodies against α 4 integrins also impairs inflammatory responses in other tissues, such as pancreatic islets and gut. 5 , 6 PML has been described in patients with . . .